Various publications, including patents, published applications, technical articles and scholarly articles are cited throughout the specification. Each of these cited publications is incorporated by reference herein, in its entirety and for all purposes.
Orthopedic implants can be manufactured using conventional subtractive methods; milling, turning, drilling or sawing. They can also be produced using additive methods where materials in crystal or granular form are melted by energy sources and layered or applied while liquid to each other to form growing structures. These additive methods as a result, leave porosities within the bulk structure that are believed to establish pathways for bone ingrowth toward facilitating integration and fusion.
Bone fusion is enhanced by fibrous tissue formation that occurs after implantation and is loaded due to patient activity. In conventional implants, the implant material includes pores and openings of various sizes and shapes, and many are specifically manufactured to have pathways or open structures intentionally built in to allow for bone growth through the openings. One limitation of pores, however, is that the loads do not follow the often tortuous pathways and channels much beyond the opening of the porous structure and, therefore, bone growth through load-induced tensile and compressive forces is linear and the benefits are only realized for short distances into the structure. This results in the porous structure actually not allowing for the bone formation to penetrate through the implant structure.
In addition, as with any contact surface, the presence of pores and openings necessarily reduces the surface area available for contact and frictional stabilization. In fact, initial bone attachment is reduced in proportion to the amount of the porosity of the material. Moreover, if the resulting structures are too small in size such that the loads imparted on the bone by the implant device exceed the strength of the bone cells, the cells begin to remodel as a result of stress-induced necrosis which is a natural healing property of bones.